As is well known in the art, gear pumps can operate effectively in systems having entrained air in the hydraulic oil. However, the entrained air in the oil creates problems, such as, cavitation. Cavitation can cause erosion of pump components, system noise, and discharge pressure ripples. The noise is basically caused by imploding or collapsing the entrained air the oil is suddenly subjected to the high pressure at the discharge side of the pump. Many attempts have made to overcome this problem. In some instances, air separators have been installed to separate the air from the oil prior to the oil entering the pump. In other instances, special porting has been added to the pump housing in order to force the entrained oil through bleed orifices back to the reservoir prior to the oil entering the discharge passage. In yet other instances, special bleed slots have been added to the pump housing to pre-pressurize the air prior to the oil and air mixture entering the discharge passage. In these instances, the slots have either been too large or too many which results in too much leakage of high pressure oil and/or too much side loading on the bearings of the pump. Likewise, in some instances the operation of machining the bleed slots is too costly.
The present invention is directed to overcoming one or more of the problems as set forth above.